When optical recording is performed on a photoconductor scanned with a plurality of laser beams simultaneously by a rotary polygon mirror in a laser printer used as a typical image forming apparatus, the recording can be speeded up correspondingly to the number of beams even if the rotation velocity of the rotary polygon mirror cannot be increased. As a method for generating a plurality of laser beams, there is a method using an optical fiber array. There has been known an image forming apparatus for performing optical recording on a photoconductor scanned with a plurality of laser beams using such an optical fiber array (for example, see JP-A-9-146023).
In a background-art optical fiber array, optical fibers themselves have manufacturing errors. When a plurality of optical fibers are arranged into an array, core portions of the optical fibers are not aligned vertically so as to be not arranged on a straight line, or the core portions are arranged at uneven intervals. It is therefore difficult to arrange the optical fiber array precisely.
When the number of beams is further increased without changing the pitch of the beams, multiple beams pass through places far from the center of a lens. Thus, aberration increases. Therefore, in order to further increase the number of beams, it is necessary to arrange the beams at a narrower pitch. In the optical fiber array, it is however difficult to make the pitch not wider than the optical fiber diameter.
Further, when a semiconductor laser array is used in place of the optical fiber array, there is a problem of thermal crosstalk. It is therefore difficult to make the pitch narrower, and it is difficult to further increase the number of beams.
However, when a plurality of laser beams emitted from the optical fiber array or the semiconductor laser array are guided into a light guide array, it is possible to obtain multiple beams arrayed at a narrower pitch and with a higher accuracy. Thus, the number of beams from the multi-beam light source can be further increased, and the beams can be arrayed precisely. It is therefore possible to perform optical recording at a high speed and with a high accuracy.
The light guide array is manufactured as follows. That is, a guide layer is formed on a substrate. Guide patterns are formed by a lithographic process, a dry etching process, or the like. After that, an over-clad layer is formed. However, when a defect appears in a part of a light guide in the light guide array, the light guide array becomes defective. Thus, the light guide array cannot be used. Further, due to a change in process conditions, it is also likely that a light guide array having an intended line width cannot be manufactured.